Sugar cane juice is an extremely complex liquid medium, containing many organic and inorganic constituents in soluble, suspended/decantable and suspended/colloidal form. Cane sugar for human consumption is produced by means of clarification of sugar cane juice using an extraction process, which is then processed and concentrated to obtain sugar.
Clarification is therefore an essential step to obtain high yields and high quality of the sugar. The clarification process needs to remove components other than sucrose and, at the same time, minimize loss of sucrose and color formation.
Sulfitation is currently the most widely used process to clarify cane juice. It consists of SO2 (sulphurous anhydride) absorption by the juice, reducing its original pH to levels between 3.7 and 4.2. The use of the sulfitation process involves: (a) inhibition reactions causing color formation; (b) coagulation of suspended colloids; and (c) formation of a precipitate of CaSO3 (calcium sulfite). Furthermore, it also reduces the viscosity of the juice and consequently of the syrup, massecuites, and molasses, facilitating evaporation and baking operations.
Nevertheless, the sulfitation process has problems which the sugar/alcohol industry would like to be solved, including (a) sucrose inversion due to low pH during the process; (b) potential environmental and external corrosion problems in the area, caused by any emission of SO2/SO3; (c) incrustation and corrosion of the evaporation equipment; and (d) presence of sulfite in the final sugar.
Another method to clarify sugar cane juice is carbonation, which generally employs treatment with lime and controlled addition of carbon dioxide (CO2). However, this process results in (a) increase in the loss of inverted sugar in the juice (fructose and glucose) due to the high alkaline pH (generally pH of about 10) and the high temperatures used for the process, adversely affecting yield of alcohol production from the final molasses, and (b) difficulty in filtering the precipitates from clarifiers, requiring a higher investment in equipment, higher operational costs and a more complex operation.
Therefore, there is a desire to have a clarification process which is superior to the sulfitation process, but which avoids the problems with carbonation. The present invention provides such a process.
Silicate microgels are used in water purification and water flow processes. WO 99/61377 discloses a process to clarify water streams containing biosolids resulting from processing food and organic residues, which comprises contact of the stream with an anionic colloid, which may be a silicate microgel, and an organic polymer to flocculate the biosolids.
For sugar cane juice clarification it is desired to minimize the accumulation of silica in the juice and in production heating equipment. The process of the present invention resolves this problem while avoiding the problems with the prior art sulfitation and carbonation processes.